1. Field of the Invention
The present invention refers to a compound of a group of compounds, each compound of the group consisting of a metallurgical combination of two or more component metals and having its specific composition and associated color. Such compounds are commonly referred to as alloys or as intermetallic compounds. The invention equally concerns a method for producing the compound of the invention, as well as the use of the compound for the manufacture of jewelry and other adorned products.
In the following each component will be referred to by its chemical symbol as appearing in the Periodic Table of Elements, e.g. Fe for iron, Au for gold, Cu for copper, etc., and each intermetallic compound will be identified by its constituent components, whereby associated coefficients and subscripts are used in conventional manner to refer to relative quantities of the components involved. Otherwise, compositions will be given in atomic %, if not stated differently.
2. Description of the Prior Art
Among the many varieties of existing intermetallic compounds some are known to display beautiful characteristic colors. A known example of such a compound is AuAl.sub.2, an alloy that has been tried to be used for the manufacture of jewelry items, watch cases, etc., at various occasions. The properties of this alloy have been described in the literature (e.g. in Zeits. Metallkunde 17, 1980, page 577) as follows: "An interesting alloy made of Au and Al is the intermetallic compound AuAl.sub.2, because of its unusual purple color. Like many other intermetallic compounds, AuAl.sub.2 is very brittle and hard at room temperature, quite resistant against oxidation and consequently not simple to form. If stored for a few weeks in the laboratory, it spontaneously disintegrates." The suggestion has been made in DE-PS No. 659 155, to add aluminum or some other soft metal to the compound AuAl.sub.2, to reduce its brittleness. The attempt has also been made to apply the metal by plasma spray or to generate a coat by chemically diffusing Al in Au. However, in such processes the reactions cannot be controlled adequately, and the metal becomes porous. Thus, the attempt to obtain a colored gold-alloy to be used for making jewelry items, has not been successful so far. Other colored intermetallic compounds have also been known, such as PtAl.sub.2, NiAl, CoAl, NiGa, PdIn or CoSi.sub.2. PtAl.sub.2 and CoAl are yellow, NiAl is blue, PdIn red, and CoSi.sub.2 blue-black. These metals, too, are usually brittle; therefore, the decorative effect of their colors cannot be put to use in the manufacture of jewelry. In addition, several of the aforementioned compounds, for example AuAl.sub.2, tend to spontaneously disintegrate in reactive media.